Magnificent Orion

This article was written by Christine
(Coutts) Clement for the Thamesville Herald in honour of IYA2009.

It was published on February 25, 2009.

This photograph of the prominent winter constellation Orion was taken
from a ranch in Arizona in the winter of 2003. It was posted as the
NASA
Astronomy Picture of the Day on February 7, 2003. Image Credit &
Copyright: Matthew Spinelli.

Throughout 2009, the International Year of Astronomy, the citizens of the
world are encouraged to discover and enjoy the day and night time skies.

One of the most beautiful constellations is Orion, which is conspicuous
in the winter sky. It is named for a gigantic hunter in Greek mythology.
Four bright stars, two representing the shoulders and two representing
the knees, outline the figure, and in the centre are three "belt" stars
with a sword hanging below them.

At the end of February, observers in Ontario see Orion prominent in
the south at around 8 p.m., but as the evening progresses it moves westward
and sets about an hour after midnight. Stars and constellations
rise in the east and set in the west every day, just like the Sun.
This daily motion is due to the Earth's rotation on its axis.

However, constellations also change their positions as the seasons
progress. If you look for Orion in the early evening at the beginning
of May, you will find that it is low in the western sky and will
set soon after. In the summer, you won't see it at all because
it sets before nightfall. This shift with the seasons occurs
because the Sun appears to move around the sky, through the constellations
of the Zodiac, over the course of a year. We see only the
constellations that are above the horizon during the night. Therefore
some constellations are visible in the winter while others are visible
in the summer. It all depends on the position of the Sun.

Thanks to the contributions of Galileo and other scientists of
the 16th and 17th centuries, we know that the Sun does not really move
around the sky. It is just a matter of perspective. As the Earth
completes its annual orbit around the Sun, the Sun appears to
move.

Nowadays, most of us spend our evenings indoors and are not familiar
with the night sky. This has not always been the case. The indigenous
peoples in North America had a much better knowledge of the
constellations: they didn't have televisions or radios to occupy them
at night and their sky was much darker than ours. Furthermore, they
didn't have clocks or calendars. Familiarity with the constellations
provided a method for keeping track of the time and the progression
of the seasons, which was important for agriculture. For example,
Aboriginal North Americans knew that when Orion sets in the western
sky at dusk, it is time to start planting.

While most constellations can only be observed in certain seasons,
there are a few that can be observed throughout the year. We call them
circumpolar constellations and we'll talk about them next time.